Impact of the lunar nodal cycle on subalpine tree growth in the North American Cordillera

We provide the first comprehensive assessment of the potential influence of the 18.6-year lunar nodal cycle (a substantial oscillation in the plane of the moon’s orbit) on subalpine tree growth in northwestern North America. This cycle impacts winter temperatures in the region, potentially in association with climate indices such as the Pacific North American pattern (PNA). Moreover, there is evidence that winter weather can impact subsequent subalpine tree growth. Here, we report evidence gleaned from archived tree-ring measurements of a potential association between the lunar nodal cycle and subalpine tree growth in conjunction with proxies for the PNA and the North Pacific Gyre Oscillation. The association between tree growth and the lunar nodal cycle is notably synchronous over a broad expanse extending from central Alaska south to Oregon. Given both sporadic evidence of such associations in Eurasia and corroborating evidence on a potential causal link through winter climate, this association warrants solid attention.